1. Field of the Invention
The present invention relates to a molding device for sealing semiconductor element with resin and a method of positioning lead frames on a molding die, and particularly to an improvement in positional adjustment between a molding die and a lead frame on which a semiconductor element is provided.
2. Description of the Prior Arts
FIG. 10 is a conceptual side view of a conventional molding device 200 for sealing a semiconductor element with resin. The device 200 is provided with a carrier plate 1 for carrying a lead frame 3 to which a semiconductor element 30 is bonded. The lead frame 3 is electrically connected to the semiconductor element 30 through wiring therebetween. The carrier plate 1 is provided with frame chucks 2 for taking up the lead frame 3 from a loader 4.
The lead frame 3 is first supplied to the device 200 by the loader 4. The lead frame 3 is grasped by the frame chucks 2, and then the carrier plate 1 goes up with the frame chucks 2 holding the lead frame 3 as shown by an arrow A. The carrier plate I is moved in the horizontal direction B until the lead frame 3 reaches a gap between a top die 6 and a bottom die 8. The top and bottom dies 6 and 8 are provided on top and bottom platens 5 and 9, respectively. Positional adjustment pins 7 are planted on the bottom die 8.
When the lead frame 3 reaches a position at which positioning holes 3a of the lead frame 3 are just above the positional adjustment pins 7, the movement of the carrier plate 1 in the direction B is stopped and then the carrier plate 1 goes down as shown by an arrow C. Consequently, the position adjustment pins 7 are inserted into holes 3a and positional alignment of the lead frame 3 to the dies 6 and 8 is attained. The chucks 2 are opened and then the carrier plate 1 goes back to the original position thereof. The top die 6 goes down and an operation for sealing the semiconductor element 30 with resin is then conducted.
In the operation of placing the lead frame 3 on the bottom die 8, however, the lead frame 3 often goes down onto the bottom die 8 without inserting the pins 7 into the holes 3a because of mechanical shock in the stop motion and thermal expansion of materials forming the lead frame 3 and the device 200. When such an error is caused, a package of the semiconductor element which is formed of resin is deviated from a predetermined position on the lead frame 3, and as a result, a defective semiconductor device is obtained. Furthermore, when the dies 6 and 8 are closed with the semiconductor element 30 inserted therebetween, the semiconductor element 30 on the lead frame 3 comes in contact with a wall in the cavity of the die 6 or 8, so that the die is damaged by the semiconductor element 30. In order to prevent these disadvantages, it has been desired to develop a device in which the lead frame 3 is positioned on the die 8 accurately.
Furthermore, the stop position of the carrier plate 1 must be re-adjusted when the type of semiconductor devices is changed, and long time is required in the conventional device 200 for the re-adjustment.